Celestial's Particle is a material added by AlchemistNPC mod, obtained by defeating the Dungeon Guardian.

It's used in crafting any 2 of Celestial Fragments and many other stuff in the mod itself.

On Normal mode, the Dungeon Guardian will drop 5-10 Particles.

When on Expert mode, it will drop 15-20 Particles.

To summon the Dungeon Guardian, you can buy the Horrifying Skull from the Jeweler.